This application is based on Japanese Patent Application No. 2001-239825 filed on Aug. 7, 2001, the disclosure of which is incorporated herein by reference.
The present invention relates to a headlamp having a discharge lamp and it is suitable for mounting on a vehicle.
Recently, a discharge lamp is used for a vehicular headlamp. The discharge lamp is an arc discharge-type lamp in which such as xenon gas is enclosed in a discharge lamp bulb (arc tube). The lamp is emitted with a discharging phenomenon generated between a pair of electrodes. The light is white near the sunlight. As compared with a conventional halogen lamp, the discharge lamp emits twice quantity of light with power saving of about 70%, thereby increasing visibility of the headlamp.
In general, a high voltage of substantially a few kV to a few tens of kV is applied to turn on a discharge lamp. After the discharge lamp is turned on, a voltage of substantially 35W is applied to the discharge lamp to maintain it lit up. Therefore, a special lighting control circuit unit is required to drive the discharge lamp. The lighting control circuit unit mainly includes a converter for increasing a direct current voltage from a battery, an inverter for exchanging the direct current voltage into an alternate current voltage and an igniter for generating high voltage of substantially a few tens kV.
In the vehicular headlamp, the lighting control circuit unit is generally mounted outside of a lamp housing. In this case, a high voltage supplying wire for supplying a high voltage to the discharge lamp and an electric connector are required. Therefore, it is difficult to downsize the unit. Also, a space for mounting the unit is required on the vehicle and mounting or fixing work is increased. Furthermore, a shielding member is required to reduce an electric noise generated by the high voltage supplying wire, thereby increasing a manufacturing cost.
To solve the above disadvantages, in a vehicular headlamp disclosed in JP-A-10-228804, for example, a lighting control circuit unit is fixed to a rear surface of a reflector in a lamp housing. An electric connector is embedded in the lighting control circuit unit and a discharge lamp bulb is directly connected to the connector.
In this kind of headlamp, when the discharge lamp bulb is exchanged, the lighting control circuit unit is removed first from the lamp housing. In the headlamp disclosed in JP-10-228804, the size of the lighting control circuit unit is relatively larger than that of an opening portion formed on the lamp housing for an exchange of the discharge lamp bulb. Therefore, when the lighting control circuit unit is removed from the lamp housing, the lighting control circuit unit is not only pulled in an axial direction of the discharge lamp bulb, but also turned or moved repeatedly in a direction different from substantially the axial direction of the discharge lamp bulb. Therefore, it takes time to remove the lighting control circuit unit. Further, the lighting control circuit unit, connector and discharge lamp bulb are integrated. Therefore, it is required to remove the lighting control circuit unit integrally with the connector and discharge lamp bulb to exchange the lighting control circuit unit. Accordingly, it takes time to exchange the lighting control circuit unit.
The present invention is made in view of the above disadvantages, and it is an object of the present invention to provide a headlamp in which a discharge lamp bulb is easily exchanged.
It is another object of the present invention to provide a headlamp in which a lighting control circuit unit is removable from a lamp housing separately from a discharge lamp bulb.
In a headlamp of the present invention, a lighting control circuit unit for driving the discharge lamp bulb is provided in a lamp housing. A discharge lamp bulb is held on a reflector. The discharge lamp bulb is directly connected to the lighting control circuit unit. The lighting control circuit unit is removable through an opening of the lamp housing while the discharge lamp bulb is fixed to the reflector.
According to the headlamp of the present invention, it is possible to remove the lighting control circuit unit separately. Therefore, the lighting control circuit unit and the discharge lamp bulb are separately and easily removed and exchanged.